In a hydraulic circuit or system of the type concerned here, an operating fluid is pressurized and delivered to a workload, such as a straight-type cylinder, to provide a linear mechanical output and then recirculated. In order to provide an output signal which is a function of an output error signal, selector valves are employed to control the direction of flow of the operating fluid to the workload. These selector valves or hydraulic relays, often take the form of a spool valve, usually constructed in either a three-way or a four-way valve-porting arrangement. The mechanical displacement of the spool allows the hydraulic pressure supply to be ported in a fashion that will displace the work cylinder in either direction, depending upon the spool displacement.
Hydraulic systems are categorized by high power gain inasmuch as liquids can be converted to high pressures or flows through the use of various types of pumps. Thus, the activation of a selector valve often results in flow irregularities and pressure surges or spikes which can cause damaging problems, such as the unintentional activation of control elements as well as line ruptures.
Heretofore, the alleviation of flow irregularities and surge problems have been accomplished by the insertion, into the hydraulic circuit, of separate surge damping valves as well as flow regulators that control the rate of flow of the operating fluid to the workload. While operationally quite efficient, the use of separate selector valves, surge damping valves and flow regulators results in system complexity which increases the cost and weight of the system as well as increasing maintenance requirements while reducing the reliability of the operation.